[141548] in North American Network Operators' Group
Re: Cogent IPv6
daemon@ATHENA.MIT.EDU (William Herrin)
Wed Jun 8 22:25:05 2011
In-Reply-To: <FC8ABE0E5D384A489CDB16C4A8EB77839B3E9C6995@MSMAIL01.LUV.AD.SWACORP.COM>
From: William Herrin <bill@herrin.us>
Date: Wed, 8 Jun 2011 22:24:31 -0400
To: Kelly Setzer <Kelly.Setzer@wnco.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Wed, Jun 8, 2011 at 9:58 PM, Kelly Setzer <Kelly.Setzer@wnco.com> wrote:
> IPv6 newbie alert!
>
> I thought the maximum prefix length for IPv6 was 64 bits,
> so the comment about a v6 /112 for peering vexed me. =A0I
> have Googled so much that Larry Page called me and
> asked me to stop.
>
> Can someone please point me to a resource that explains
>how IPv6 subnets larger than 64 bits function and how
>they would typically be used?
Hi Kelly,
IPv6 netmasks work exactly like IPv4 netmasks. You can even route
/128's if you want. Two major caveats:
1. SLAAC (stateless autoconfiguration, the more or less replacement
for DHCP) only works if the subnet on your LAN is exactly /64. So
unless you're manually configuring the IPv6 address on every machine
on your subnet, you're using a /64.
2. Reverse DNS delegates every 4 bits (in IPv4 its every 8 bits). And
when you write the address, every 4 bits is one digit. So unless you
want to make things needlessly hard, you're also going to choose 4-bit
boundaries for everything. I.e. a /56 or a /60 but never a /57.
Now, as to why they'd choose a /112 (65k addresses) for the interface
between customer and ISP, that's a complete mystery to me.
Regards,
Bill Herrin
--=20
William D. Herrin ................ herrin@dirtside.com=A0 bill@herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004
